Hi there,
Cats are pretty hardy. Any genetic issues like weakness in the immune system will be apparant when the kitten are four or five weeks old.If they are ill, they will sneeze and have eye and nasal dicscharge
If they are happy, healthy and nursing or eating fine you don't have to worry.
Best of luck to you,
Terri
Feline Healthcare Expert
Expert in feline health and behavior. 20 years experience with cats.